1. Field of the Invention
The invention relates to detection of motion. In some aspects, the invention relates to detection of laboratory animal motion.
2. Description of the Related Art
In the discovery of neurological drugs, e.g., analgesics, many animal pain models are used. In one such model, a small amount of formalin is injected into one rear paw of a rat. The resulting irritation causes the rat to lick and/or to shake this paw in a repetitive, flinch-like motion. This reaction is considered a painful response. A test compound is administered to the rat after the formalin injection and changes in paw motion counts are used to assess the compound's analgesic effect. In other tests, a rat paw is exposed to a heat source and the motion of the paw is monitored as the rats are exposed to various neurological compounds. Such tests can be used to screen analgesic compounds or to perform other neurological experiments.
Currently, the most commonly used instrumentation for detecting rat paw motion employs a metal detector to sense the motion of a metallic bracelet attached to a paw. With reference to FIG. 1, a metal detector typically consists of two induction coils. A transmitter coil 100 is energized with a relatively low-frequency (5-10 KHz) AC signal. A receiver coil 110 is concentric and coplanar with the transmitter coil 100. The coils are only weakly coupled through free space. When a small piece of metal (e.g., a rat paw bracelet 120) is introduced into the area above the two coils, the coupling is increased and a stronger signal is detected by the receiver coils 110. The metallic bracelet 120 concentrates the magnetic flux so that more field lines are captured by the receiver coil 110, giving rise to a stronger detected signal. As this design relies on the phenomenon of flux concentration, bracelets made from high magnetic permeability metals give rise to the largest signals. Overall, this effect is weak and a very high level of amplification is needed to detect it.
In a typical laboratory environment, this design suffers from several disadvantages. First, there is usually a significant amount of metal in a typical lab, often causing mistriggering of the device. For example, wristwatches worn by the operators are a common source of interference. Second, the receiver coil's 110 cross-section is large and a very high level of amplification is used causing stray magnetic fields from various power sources to elicit false signals. Third, multiple detectors cannot be placed too close to each other because stray magnetic induction from one unit tends to falsely trigger its nearest neighbors. Thus, there is a need for improved motion detectors, particularly for use in detecting rodent paw motion.